The present invention relates to a liquid detergent composition, and to be precise, it relates to a liquid detergent composition which is mild on the human skin and is superior in detergency, oil-solubilizing power and solution stability.
As a liquid detergent composition in the prior art, there is known a composition prepared by mixing alkylbenzene sulfonate with N-acylaminoacid or the like (See Japanese Patent Publication No. 4256/1971). This liquid detergent is intended to make the best use of the superior detergency of the alkylbenzene sulfonate while alleviating the skin-irritating property inherent in said surface active agent by means of N-acylaminoacid or the like, but the anticipated result is not necessarily realized thereby. On the other hand, as a liquid detergent composition having a lower skin-irritating property, there is known a composition prepared by mixing N-acyl glutamate with alkyl betaine or amine oxide. However, this liquid detergent is not free from the defect that it is insufficient in detergency and oil-solubilizing power.
In short, in liquid detergents, the detergency and the skin-irritating property are generally inconsistent with each other, and in the prior art, it has been practically impossible to make high detergency compatible with low skin-irritating property. The inventors have made a series of studies aiming at developing a liquid detergent having superior detergency and a minimum skin-irritating property, and as a result, they have come to a finding that, when an anionic surface active agent of the polyoxyalkylene alkyl ether sulfate type and a cationic surface active agent of a specific quaternary ammomium salt type are compounded at a specific mol ratio and in specific quantities, the resulting liquid detergent composition is mild on the skin and is nevertheless superior in detergency, oil-solubilizing power and solution stability.
In this connection, the conception of combining a polyoxyalkylene alkyl ether sulfate and a cationic surface active agent of quaternary ammonium salt type is disclosed in Japanese Unexamined Patent Publication No. 35203/1977 on a transparent liquid shampoo, but the combination of an anionic surface active agent and a cationic surface active agent disclosed therein utterly differs from that in the present invention in respect of the number of carbon atoms of the long-chain alkyl radical in the cationic surface active agent employed.